import jsPDF from 'jspdf'
import html2canvas from 'html2canvas'

/*
 * 使用说明
 * ele:需要导出pdf的容器元素(dom节点 不是id)
 * pdfFileName: 导出文件的名字 通过调用outPutPdfFn方法也可传参数改变
 * splitClassName: 避免分段截断的类名 当pdf有多页时需要传入此参数 , 避免pdf分页时截断元素  如表格<tr class="itemClass"></tr>
 * 调用方式 先 let pdf = new PdfLoader(ele, 'pdf' ,'itemClass');
 * 若想改变pdf名称 pdf.outPutPdfFn(fileName);  outPutPdfFn方法返回一个promise 可以使用then方法处理pdf生成后的逻辑
 * */
class PdfLoader {
  constructor(ele, pdfFileName, splitClassName) {
    this.ele = ele
    this.pdfFileName = pdfFileName
    this.splitClassName = splitClassName
    this.A4_WIDTH = 595
    this.A4_HEIGHT = 842
  }

  async getPDF(resolve, reject) {
    let ele = this.ele
    let pdfFileName = this.pdfFileName
    let eleW = ele.offsetWidth // 获得该容器的宽
    let eleH = ele.scrollHeight // 获得该容器的高
    let eleOffsetTop = ele.offsetTop // 获得该容器到文档顶部的距离
    let eleOffsetLeft = ele.offsetLeft // 获得该容器到文档最左的距离
    let canvas = document.createElement('canvas')
    let abs = 0
    let win_in =
      document.documentElement.clientWidth || document.body.clientWidth // 获得当前可视窗口的宽度（不包含滚动条）
    let win_out = window.innerWidth // 获得当前窗口的宽度（包含滚动条）
    if (win_out > win_in) {
      abs = (win_out - win_in) / 2 // 获得滚动条宽度的一半
    }
    canvas.width = eleW * 2 // 将画布宽&&高放大两倍
    canvas.height = eleH * 2
    let context = canvas.getContext('2d')
    // context.scale(2, 2) // 增强图片清晰度
    context.translate(-eleOffsetLeft - abs, -eleOffsetTop)
    html2canvas(ele, {
      dpi: 100, // 设置截图的分辨率
      scale: 1.4 // 设置截图缩放比例，以适应pdf的dpi
    })
      .then(async (canvas) => {
        let contentWidth = canvas.width
        let contentHeight = canvas.height
        //一页pdf显示html页面生成的canvas高度;
        let pageHeight = (contentWidth / this.A4_WIDTH) * this.A4_HEIGHT // 这样写的目的在于保持宽高比例一致 pageHeight/canvas.width = a4纸高度/a4纸宽度// 宽度和canvas.width保持一致
        //未生成pdf的html页面高度
        let leftHeight = contentHeight
        //页面偏移
        let position = 0
        //a4纸的尺寸[595,842],单位像素，html页面生成的canvas在pdf中图片的宽高
        let imgWidth = this.A4_WIDTH - 10 //-10为了页面有右边距
        let imgHeight = (this.A4_WIDTH / contentWidth) * contentHeight
        let pageData = canvas.toDataURL('image/jpeg', 1.0)
        let pdf = jsPDF('', 'pt', 'a4')
        //有两个高度需要区分，一个是html页面的实际高度，和生成pdf的页面高度(841.89)
        //当内容未超过pdf一页显示的范围，无需分页
        if (leftHeight < pageHeight) {
          //在pdf.addImage(pageData, 'JPEG', 左，上，宽度，高度)设置在pdf中显示；
          pdf.addImage(pageData, 'JPEG', 5, 0, imgWidth, imgHeight)
          // pdf.addImage(pageData, 'JPEG', 20, 40, imgWidth, imgHeight);
        } else {
          // 分页
          while (leftHeight > 0) {
            pdf.addImage(pageData, 'JPEG', 5, position, imgWidth, imgHeight)
            leftHeight -= pageHeight
            position -= this.A4_HEIGHT
            //避免添加空白页
            if (leftHeight > 0) {
              pdf.addPage()
            }
          }
        }
        pdf.save(pdfFileName + '.pdf', { returnPromise: true }).then(() => {
          //去除添加的空div 防止页面混乱
          let doms = document.querySelectorAll('.emptyDiv')
          for (let i = 0; i < doms.length; i++) {
            doms[i].remove()
          }
        })
        this.ele.style.height = ''
        resolve({ out: true, loading: false }) //导出成功
      })
      .catch((err) => {
        reject({ out: false, loading: false }) //导出失败
      })
  }

  async outPutPdfFn(pdfFileName) {
    return new Promise((resolve, reject) => {
      this.ele.style.height = 'initial'
      pdfFileName ? (this.pdfFileName = pdfFileName) : null
      let target = this.ele
      let pageHeight = (target.scrollWidth / this.A4_WIDTH) * this.A4_HEIGHT
      // 获取分割dom，此处为class类名为item的dom
      let domList = document.getElementsByClassName(this.splitClassName)
      // 进行分割操作，当dom内容已超出a4的高度，则将该dom前插入一个空dom，把他挤下去，分割
      let pageNum = 1 //pdf页数
      let eleBounding = this.ele.getBoundingClientRect()
      for (let i = 0; i < domList.length; i++) {
        let node = domList[i]
        let bound = node.getBoundingClientRect()
        let offset2Ele = bound.top - eleBounding.top
        let currentPage = Math.ceil(
          (bound.bottom - eleBounding.top) / pageHeight
        ) //当前元素应该在哪一页
        if (pageNum < currentPage) {
          pageNum++
          let divParent = domList[i].parentNode // 获取该div的父节点
          let newNode = document.createElement('div')
          newNode.className = 'emptyDiv'
          newNode.style.background = 'white'
          newNode.style.height =
            pageHeight * (pageNum - 1) - offset2Ele + 50 + 'px' //+30为了在换下一页时有顶部的边距
          newNode.style.width = '100%'
          let next = domList[i].nextSibling // 获取div的下一个兄弟节点
          // 判断兄弟节点是否存在
          if (next) {
            // 存在则将新节点插入到div的下一个兄弟节点之前，即div之后
            divParent.insertBefore(newNode, node)
          } else {
            // 不存在则直接添加到最后,appendChild默认添加到divParent的最后
            divParent.appendChild(newNode)
          }
        }
      }
      // 异步函数，导出成功后处理交互
      this.getPDF(resolve, reject)
    })
  }
}

function downloadPDF(ele, pdfName, className) {
  let pdf = new PdfLoader(ele, 'pdf', className)
  return pdf.outPutPdfFn(pdfName)
}

export default {
  downloadPDF
}
